当我想编写像此平台上不存在的GetTicketCount64这样的函数时,Windows XP下会出现问题.这是我的测试代码:
uint64_t GetTickCountEx()
{
#if _WIN32_WINNT > _WIN32_WINNT_WINXP
return GetTickCount64();
#else
// http://msdn.microsoft.com/en-us/library/windows/desktop/dn553408.aspx
LARGE_INTEGER Frequency = {};
LARGE_INTEGER Counter = {};
BOOST_VERIFY(QueryPerformanceFrequency(&Frequency));
BOOST_VERIFY(QueryPerformanceCounter(&Counter));
return 1000 * Counter.QuadPart / Frequency.QuadPart;
#endif
}
for (int i = 0; ++i < 1000; Sleep(30000))
{
const auto utc = time(nullptr); // System time
const auto xp = GetTickCount(); // API of Windows XP SP3
const auto ex = GetTickCountEx(); // Performance counter
const auto diff = ex - xp;
printf("%lld %I32u %I64u %I64u \n", utc, xp, ex, diff);
}
我无法理解以下结果.从这篇文章来看,Angstrom的回复似乎不正确.最后一栏表明,随着时间的推移,GTC和GPC的差异越来越大!......几小时后它会达到零吗？
所以,我的问题是:我的GetTickCount64实现是否正确,为什么？
1401778679 503258484 503355416 96932
1401778709 503288484 503385374 96890
1401778739 503318484 503415354 96870
1401778769 503348484 503445289 96805
1401778799 503378484 503475274 96790
1401778829 503408484 503505272 96788
1401778859 503438484 503535245 96761
1401778889 503468500 503565210 96710
1401778919 503498500 503595143 96643
1401778949 503528500 503625137 96637
1401778979 503558500 503655100 96600
1401779009 503588500 503685069 96569
1401779039 503618500 503715069 96569
1401779069 503648500 503745006 96506
1401779099 503678500 503774951 96451
1401779129 503708500 503804958 96458
1401779159 503738500 503834943 96443
1401779189 503768500 503864911 96411
1401779219 503798500 503894792 96292
1401779249 503828500 503924759 96259
1401779279 503858500 503954607 96107
1401779309 503888500 503984607 96107
1401779339 503918500 504014392 95892
1401779369 503948500 504044362 95862
来自coreinfo.exe的 CPU核心信息:Coreinfo v3.21 - 系统CPU和内存拓扑的转储信息版权所有(C)2008-2013 Mark Russinovich Sysinternals - www.sysinternals.com
Intel(R) Core(TM) i3 CPU M 380 @ 2.53GHz
x86 Family 6 Model 37 Stepping 5, GenuineIntel
HTT * Hyperthreading enabled
HYPERVISOR - Hypervisor is present
VMX * Supports Intel hardware-assisted virtualization
SVM - Supports AMD hardware-assisted virtualization
EM64T * Supports 64-bit mode
SMX - Supports Intel trusted execution
SKINIT - Supports AMD SKINIT
NX * Supports no-execute page protection
SMEP - Supports Supervisor Mode Execution Prevention
SMAP - Supports Supervisor Mode Access Prevention
PAGE1GB - Supports 1 GB large pages
PAE * Supports > 32-bit physical addresses
PAT * Supports Page Attribute Table
PSE * Supports 4 MB pages
PSE36 * Supports > 32-bit address 4 MB pages
PGE * Supports global bit in page tables
SS * Supports bus snooping for cache operations
VME * Supports Virtual-8086 mode
RDWRFSGSBASE - Supports direct GS/FS base access
FPU * Implements i387 floating point instructions
MMX * Supports MMX instruction set
MMXEXT - Implements AMD MMX extensions
3DNOW - Supports 3DNow! instructions
3DNOWEXT - Supports 3DNow! extension instructions
SSE * Supports Streaming SIMD Extensions
SSE2 * Supports Streaming SIMD Extensions 2
SSE3 * Supports Streaming SIMD Extensions 3
SSSE3 * Supports Supplemental SIMD Extensions 3
SSE4a - Supports Sreaming SIMDR Extensions 4a
SSE4.1 * Supports Streaming SIMD Extensions 4.1
SSE4.2 * Supports Streaming SIMD Extensions 4.2
AES - Supports AES extensions
AVX - Supports AVX intruction extensions
FMA - Supports FMA extensions using YMM state
MSR * Implements RDMSR/WRMSR instructions
MTRR * Supports Memory Type Range Registers
XSAVE - Supports XSAVE/XRSTOR instructions
OSXSAVE - Supports XSETBV/XGETBV instructions
RDRAND - Supports RDRAND instruction
RDSEED - Supports RDSEED instruction
CMOV * Supports CMOVcc instruction
CLFSH * Supports CLFLUSH instruction
CX8 * Supports compare and exchange 8-byte instructions
CX16 * Supports CMPXCHG16B instruction
BMI1 - Supports bit manipulation extensions 1
BMI2 - Supports bit manipulation extensions 2
ADX - Supports ADCX/ADOX instructions
DCA - Supports prefetch from memory-mapped device
F16C - Supports half-precision instruction
FXSR * Supports FXSAVE/FXSTOR instructions
FFXSR - Supports optimized FXSAVE/FSRSTOR instruction
MONITOR * Supports MONITOR and MWAIT instructions
MOVBE - Supports MOVBE instruction
ERMSB - Supports Enhanced REP MOVSB/STOSB
PCLULDQ - Supports PCLMULDQ instruction
POPCNT * Supports POPCNT instruction
LZCNT - Supports LZCNT instruction
SEP * Supports fast system call instructions
LAHF-SAHF * Supports LAHF/SAHF instructions in 64-bit mode
HLE - Supports Hardware Lock Elision instructions
RTM - Supports Restricted Transactional Memory instructions
DE * Supports I/O breakpoints including CR4.DE
DTES64 * Can write history of 64-bit branch addresses
DS * Implements memory-resident debug buffer
DS-CPL * Supports Debug Store feature with CPL
PCID * Supports PCIDs and settable CR4.PCIDE
INVPCID - Supports INVPCID instruction
PDCM * Supports Performance Capabilities MSR
RDTSCP * Supports RDTSCP instruction
TSC * Supports RDTSC instruction
TSC-DEADLINE - Local APIC supports one-shot deadline timer
TSC-INVARIANT * TSC runs at constant rate
xTPR * Supports disabling task priority messages
EIST * Supports Enhanced Intel Speedstep
ACPI * Implements MSR for power management
TM * Implements thermal monitor circuitry
TM2 * Implements Thermal Monitor 2 control
APIC * Implements software-accessible local APIC
x2APIC - Supports x2APIC
CNXT-ID - L1 data cache mode adaptive or BIOS
MCE * Supports Machine Check, INT18 and CR4.MCE
MCA * Implements Machine Check Architecture
PBE * Supports use of FERR#/PBE# pin
PSN - Implements 96-bit processor serial number
PREFETCHW * Supports PREFETCHW instruction
Maximum implemented CPUID leaves: 0000000B (Basic), 80000008 (Extended).
Logical to Physical Processor Map:
*-*- Physical Processor 0 (Hyperthreaded)
-*-* Physical Processor 1 (Hyperthreaded)
Logical Processor to Socket Map:
**** Socket 0
Logical Processor to NUMA Node Map:
**** NUMA Node 0
Logical Processor to Cache Map:
*-*- Data Cache 0, Level 1, 32 KB, Assoc 8, LineSize 64
*-*- Instruction Cache 0, Level 1, 32 KB, Assoc 4, LineSize 64
*-*- Unified Cache 0, Level 2, 256 KB, Assoc 8, LineSize 64
-*-* Data Cache 1, Level 1, 32 KB, Assoc 8, LineSize 64
-*-* Instruction Cache 1, Level 1, 32 KB, Assoc 4, LineSize 64
-*-* Unified Cache 1, Level 2, 256 KB, Assoc 8, LineSize 64
**** Unified Cache 2, Level 3, 3 MB, Assoc 12, LineSize 64
您无法比较两个计时源,它们在PC中具有截然不同的实现.
GetTickCount()来自时钟节拍中断,这是由实时时钟产生的信号.传统上是专用芯片,最初是摩托罗拉MC146818,现在集成在南桥.它有一种用于手表的振荡器,晶体稳定,通常以32768赫兹运行.当机器电源关闭,锂电池或超级电容器耗尽时,此振荡器保持运行.
所以分辨率是相当恶劣的,但它是由非常受周期性地再同步与时间服务器提供时间的时钟准确,很好的长期稳定性,大多数Windows机器使用time.windows.com.查看GetSystemTimeAdjustment()以获取详细信息.
QueryPerformanceCounter()使用芯片组中可用的频率源.传统上8053计数器运行在1193182 Hertz.如今HPET定时器HAL(硬件抽象层)允许系统集成商选择他可用的任何频率源.在较便宜的设计中使用CPU时钟并不罕见.
因此分辨率非常高,但它不准确,并且没有校准此计时器的机制.从报告的QPF中减去800 ppm并不罕见.此计时器应仅用于短间隔测量,例如探测器将使用的那种.
所以不,使用QueryPerformanceCounter()作为GetTickCount64()的替代方案并不是一个好主意,除非你可以忍受不准确.从技术上讲,只要跟踪GetTickCount()溢出的值,就可以合成自己的64位计数器.例如,当前一个值为负且新值为正时,您可以增加课程计数,表明它已溢出.唯一的要求是您经常对GetTickCount()进行抽样,以便在24天内至少看一次过渡.